Crystal diode



p 1957 J. J. KASTNER ETAL 2,806,188

CRYSTAL DIODE Filed May 12, 1954 INVENTORSZ JOHN J. KASTNER IGNACE c. MOZINA 5% w 9 10) BY ATT'YS nited States Patent Othce CRYSTAL DIGDE John J. Kastner and Ignace C. Mozina, @glesby, Ill. Application May 12, 1954, Serial No. 429,194 13 Claims. (Cl. 31'7-236) This invention relates to crystal diodes, point contact transistors, and similar devices, and particularly to-improvements in the construction of such devices for obtaining and maintaining precise point contact engagement between the crystal and a coacting electrode.

The main objects of this invention are to provide an improved point contact diode; to provide an improved crystal diode or point contact transistor construction; to provide a crystal diode or point contact transistor having improved operating characteristics; to provide such a device having a more rugged construction that is substantially immune to physical shock; to provide such a device capable of maintaining precise point contact engagement between the crystal and its coacting electrode under extreme ranges of operating conditions; to provide such a device having greater sensitivity and greater stability of current; to provide such a device that is free from microphonic defects and which when used as a detector is free from hum and other disturbing noises; and to provide such a device that is substantially unaffected by temperature changes.

Further objects of this invention are to provide an improved crystal diode or point contact transistor construction that is more easily assembled in manufacture, and which can be made at a greatly reduced cost as compared to such devices as heretofore known; to provide such a construction that will withstand much greater ranges of temperature change without loss of efliciency or eflectiveness; to provide such a construction which, when heated to or beyond the point where operativeness ceases, will upon cooling automatically reset the point contact relationship between the crystal and the coacting electrode without loss of sensitivity or other deterioration of its normal operating characteristics; and to provide an improved crystal diode wherein a relatively low-cost galena crystal may be employed, instead of the more expensive materials usually used, without any sacrifice of sensitivity, stability of current, or noise-free operational characteristics.

A specific embodiment of this invention is shown in the accompanying drawings, in which:

Figure l is a perspective view of the improved diode in a more or less conventional form, and

Fig. 2 is a sectional view of the same, as taken on line 22 of Fig. 1, illustrating the improved construction of the device.

In the form shown in the drawings the improved diode construction comprises a tubular housing or shell 1, made of any suitable moisture proof material, within which is mounted a solid slug or plug 2 of a suitable electrically conductive material, on the inner end of which a suitable crystal 3 is firmly secured. A pigtail or terminal wire 4, suitably attached to the plug 2, extend outwardly from one end of the tubular body or shell 1 and, as shown, the crystal plug 2 is secured in the shell 1 by means of a closure or sealing cap 5 made of any suitable sealing material such as a hard plastic sealer or cement.

The electrode or cat-whisker 6, which coacts with the 2,806,188 Patented Sept. 10, 1957 crystal 3, is inserted into the housing or body 1, from the end opposite the pigtail 4, into point contact engagement with the crystal 3, and the inner portion of the whisker 6 is embedded in and surrounded by a specially compounded plastic material which forms a retaining body 7 wholly embedding the contacting end of the whisker 6 and the adjacent surface of the crystal 3. The whisker end of the body 1 is then finally filled and closed by means of a suitable sealing material or cement 8 which is preferably of the same nature as the sealing plug 5 at the opposite end of the device.

As shown in Fig. 2, the whisker 6 is provided with two axially spaced right-angular U-shaped return-bends 9 and 10 which are located within the body 1 and along the length of the whisker, so that the inner one of the U-shaped bends will be embedded in the specially compounded plastic body 7, and the other U-shaped bend will be embedded in the sealing material or end plug 3. The purpose of these U-shaped return-bends in the whisker is to firmly lock the whisker 6 to the sealing plug 8, so that it cannot be physically pulled out of the diode body, and to interlockingly engage the inner end of the whisker with the special plastic contact embedding body 7.

A particular feature of the invention, from which the improved results are apparently derived, is the specially compounded plastic body 7 which encloses or embeds the inner or contacting end of the whisker electrode 6 and the contacting surface of the crystal 3. This body 7 is formed from a mixture of a suitable thermoplastic material in granular form and a thermosetting plastic material in fluid form, with or without a suitable filler of inert material, the composition being mixed together at room temperature and then poured while fluid into the interior of the body or shell 1, on top of the crystal 3, to a depth suflicient to include the innermost return-bend 9 of the whisker when the whisker is in crystal engaging position. The fluid theimosetting material is provided with a suitable accelerator which causes it to harden and set at room temperature within a relatively short time and the body 7 thus becomes a substantially rigid unit in situ.

The thermoplastic material may be any suitable dielectric such as protein, vinyl, acrylic, or cellulosic plastic material, however, we prefer to use a clear polystyrene molding material such as clear Bakelite XMS 10023. This material in solid form is ground, crushed or otherwise comminuted to a granular form, in which the grains or pieces are about the size of fine sand. The thermosetting material of the compound may be any suitable dielectric, such as a celanese, phenolic, or amino resin in fluid form and for such we prefer Marco celanese resin (MRZSc resin), to which a paste catalyst (Me I) and a suitable accelerator, such as celanese accelerator E has been added. Any suitable inert filling material may be employed as a filler for the plastic mixture or compound and for this purpose we prefer to use silica sand, although ground quartz, asbestos, mica, glass fiber, or other suitable inert materials may be employed. Preferably, the filler material will be ground to a size not greater than the granular thermoplastic so that it will mix uniformly with the latter, and we have successfully used fillers ground to a size varying from the fineness of flour to the coarseness of sand.

Preferably the granular thermoplastic material and the fluid thermosetting material are mixed in a one to one ratio by volume, and the ratio of the plastic mixture to the inert filler materials is likewise one to one by volume. That is, the compound is preferably formed with one part granular thermoplastic material, one part fluid thermosetting material, and two parts ground inert filler material, the ratio of the elements being by volume.

It should be understood, however, that the relative amounts of the materials comprising the composition may be varied considerably. For example, the proportions of thermoplastic to thermosetting materials may range from four parts thermoplastic and one part thermosetting, to one part thermoplastic and four parts thermosetting. Also, the proportion of plastic material to inert filler material may vary over a considerable range, and in this regard we have successfully used compositions varying from all plastic material and no filler material, to one part plastic material and two parts filler material.

The thermoplastic-thermosetting material composition when once it has been poured and solidified about the contacting end of the whisker 6 and the contact surface of the crystal 3, being moisture proof and dielectric, not;

diode elements against disturbance from substantially any outside influences or forces, the body 7 forming a normally rigid, solid plug-like structure which becomes bonded to all of the internal surfaces of the diode structure with which it contacts. Initially, the thermoplastic material in granular form, functions in the same manner as the inert filler material to extend the mass of the body of the plug 7, and the thermosetting material serves initially as a binder to cement or bond all of the particles of granular material into an integral body. Also, the thermosetting material, upon hardening by polymerization, retains the form to which it has hardened and be-- comes a substantially rigid skeletal frame which holds the thermoplastic granules in uniformly distributed relation and is substantially impervious to the effect of mois ture and temperature changes. Thus in the composition forming the body 7, the thermosetting material functions to permanently seal and support the entire composition as one unitary or solid mass. On the other hand, the granules of thermoplastic material do not necessarily remain solid. Rather they are subject to softening and hardening by changing temperature conditions and may be softened and then hardened repeatedly.

The granular thermoplastic material is not chemically combined with the thermosetting material during mixture of the composition, but rather is an additive which retains its identity the same as the inert filler material; As a result when the entire composition becomes hardened the thermoplastic will be found to be uniformly dispersed throughout the body 7 in the form of individual grains or aggregate, as indicated by the elements 11 appearing in Fig. 2. r

In the event, however, suflicient heat is applied to the diode body, or the diode becomes overheated in operation, the thermoplastic material'will soften or melt, resulting in a change in the internal pressure of the body 7, and hence a change of the pressure at the point-contact between the whisker 6 and the crystal 3 so that the contact relation is lost and the diode becomes inoperative. Upon cooling, however, the thermoplastic material will re-form as individual solid grains and, in the process, the body 7 will return to its original state so as to automatically reset the whisker-crystal contact of the diode to its normal operating condition.

t is this function of the thermoplastic material to reset itself upon cooling, after it has been subjected to overheating of the diode assembly, which permits the diode to regain its operativeness, and to function with the same degree of sensitivity, stability of current and lack of extraneous noises or hums that characterizes the original assembly; whereas in any other diode construction, overheating of the assembly will so disturb the whisker-crystal relationship as to ruin the diode for any further useful purpose. Thus with our improved construction, the diode assembly is not only secure against-physical shock, but is also substantially incapable of being permanently in capacitated through overheating.

In the manufacture of the improved diode construction, the crystal '3 is permanentlymounted in the slug or supporting body 2 in the usual manner, by casting solder, lead or any other suitable conductive material, so as to embed the crystal in one end of the slug with one face of the crystal exposed. Simultaneously the pigtail 4 is cast into the slug body 2, so that the crystal 3, slug body 2, and pigtail 4, form a preassembled unit. This unit is then mounted in one end of the tubular sleeve or shell 1, which may be cut from pre-formed tubular stock, and is secured in place by means of the cap 5 of a suitable sealing material. The slug body 2 is formed to fit the interior of the shell or housing 1, and the crystal 3 is substantially centrally located so that its exposed surface will face axially toward the open end of the shell 1.

The plastic composition 7, having been previously mixed and in fluid state, is then poured into the open end of the body 1, to a depth-of about one-third the length of the body, and while the plastic composition is still soft the whisker 6 is inserted through the open end of the body 1 and pushed through the composition material until its tip end is engaged with the crystal 3. The whisker 6 is then shifted over the surface of the crystal '3 until the best point of contact is found, as determined by suitable test equipment not shown or described, after which the Whisker 6 is held stationary until the plastic composition body 7 has become hardened or set. The time required for setting the plastic composition is determined by the amount of accelerator used with the thermosetting material and is preferably but little more than that required to pour one batch of the mixture and adjust the whiskercrystal contact relation in ordinary production procedure. The assembly is then finally sealed by means of the cap 8 of suitable sealing material or cement, and the construction of the diode is thereupon complete.

As shown in Fig. 2 the right-angled, U-shaped returnbends 9 and 10, axially spaced along the length of the whisker 6, are located so that the first U-shapecl bend 9 is engaged in the plastic composition body 7, and the second U-shaped bend it is rigidly engaged in the end cap 8. Thus the whisker 6 becomes an integral part of the diode assembly, and its point-contact engagement with the crystal 3 is secured against disturbance by any force or strain that might be applied to the projecting or terminal end of the whisker 6. Also, since the innermost U -shaped bend 9 of the whisker is interlockingly engaged with the plastic composition body 7, the inner end of the whisker and particularly its point-contact engagement with the crystal 3, is securely held so as to be immune from any disturbance due to vibration or shock.

Under normal conditions the plastic composition body 7 is a solid and rigid unit, and the tip of the whisker 6 is rigidly held 'at the best point of engagement with the crystal 3 and at the exact degree of contact pressure for 'which the whisker was initially adjusted before the composition body 7 became hard. Upon overheating of the diode assembly, however, which in the case of ordinary diode construction would render the diode'permanently disabled, the thermoplastic material 'of the composition comprising the body 7, becomes soft and semi-fluid so as to absorb any stresses or distortion forces that may develope in the cellular skeleton frame of thermosetting material which surrounds, bonds, and interlocks the particles of thermoplastic material. Thus, even though the diode contact engagement may be temporarily disabled, or rendered inoperative, by excessive temperature conditions, as soon as the assembly cools to its normal temperature the thermoplastic material hardens and resets itself so as to return the internal structure of the composition body 7 to its original state, whereupon the contacting tip of the whisker 6 is again brought into engagement with the crystal 3 at exactly the same point and with the same contacting pressure that the whisker originally adjusted.

It will thus be seen that because of the improved composition body 7, which surrounds and retains the whiskercrystal contacting engagement and relationship, the contact of the whisker with the crystal 3, is not only permanently maintained, but is also positively sealed against any disturbance from external influences, including shock, vibration and temperature changes, so that the diode construction is substantially indestructible. It is also believed that this embedding of the contacting surfaces between the whisker 6 and the crystal 3, in the particular plastic composition body 7 which we employ, is one of the principal factors whereby a crystal diode is realized which is free from any hum, extraneous noise, or other microphonic effects.

In the construction of our improved diode, we prefer to make the body or shell 1 of a dielectric thermosetting plastic material, which is readily available in stock tubular form, from which sections can be easily cut to form the body shells. As before-mentioned, however, it will be understood that any suitable dielectric material may be employed for the body 1, such as the many commercially available plastics as well as porcelain, metal or fiber. The crystal 3 may be of galena, germanium, or silicon, or any other suitable semi-conductor material. Preferably we use galena as the crystal material since it is the cheapest of the materials of which we know and because, with our improved diode construction, galena will produce perfect results comparable with or better than those obtained from germanium or silicon. This ability of our improved diode to obtain the highest quality of results. by using galena crystals instead of the more expensive germanium or silicon is believed to be a very important feature of our invention.

For the pigtail 4 we prefer to use tinned, soft copper wire, having a diameter of .025 inch, however, steel wire, bronze wire, brass wire, or any other suitable conductor material have a size range of .005 to .060 inch may be employed. For the whisker 6, we prefer to use music wire of .011 inch diameter. However, wire of steel, bronze, brass or copper may also be employed and the size range may vary from .005 to .060 inch.

The improved diode may be made in substantially any size or shape depending upon the uses to which it is to be put. However, one of the particular advantages of our present invention is that the diode units can be made extremely small. For example, one of our particularly successful products is a diode of the improved construction having a diameter of five-sixteenths inch and a body length of one-half inch, the internal diameter of the body being one-quarter inch.

The main advantages of our invention reside in the substantially indestructible construction of improved diode unit, and in the fact that the device is not rendered permanently inoperative by being subjected to excessive temperature conditions; in the fact that the improved diode can be made from cheaper materials than those heretofore employed; in the fact that galena may be used as the crystal element and yet obtain the highest quality of performance; and in the fact that the improved diode can be manufactured on a production basis on a much less cost than any of the diode devices presently known.

Other particular advantages of our improved diode construction reside in its greater sensitivity, its greater stability of current, and the substantially complete absence of any hum or other microphonic effects; and in the fact that regardless how often the improved diode may become overheated to the point of inoperativeness, the device will always upon cooling return to precisely the point of crystal contact and contacting pressure at which the crystal engaging whisker was initially set.

Although but one specific embodiment of this invention has been herein shown and described, it will be understood that numerous details of the construction shown may be altered or omitted without departing from the spirit of this invention as defined by the following claims:

We claim:

1. A point-contact crystal electrode device comprising a hollow shell having a crystal of semi-conductor material mounted therein, a whisker of conductive material mounted in said shell in point-contact relation with a surface of said crystal, a body of dielectric material embedding the contacting end of said whisker and said surface of said crystal, said body comprising a substantially uniform mixture of thermoplastic and thermosetting materials integrally bonded to form a rigid unit, and terminal means leading from said crystal and said whisker for connecting the same in an electric circuit.

2. A point-contact crystal electrode device comprising a hollow shell having a crystal of semi-conductor material mounted therein, a whisker of conductive material mounted in said shell in point-contact relation with a surface of said crystal, a body of dielectric material embedding the contacting end of said whisker and said surface of said crystal, said body comprising a substantially uniform mixture of thermoplastic and thermosetting materials integrally bonded to form a rigid unit, one of said materials being of granular form, and terminal means leading from said crystal and said whisker for connecting the same in an electric circuit.

3. A point-contact crystal electrode device comprising a hollow shell having a crystal of semi-conductor material mounted therein, a whisker of conductive material mounted in said shell in point-contact relation with a surface of said crystal, a body of dielectric material embedding the contacting end of said whisker and said surface of said crystal, said body comprising a substantially uniform mixture of thermoplastic and thermosetting materials integrally bonded to form a rigid unit, said thermoplastic material being of granular form and integrally bonded in said body by the thermosetting material, and terminal means leading from said crystal and said whisker for connecting the same in an electric circuit.

4. A point-contact crystal electrode device comprising a hollow shell having a crystal of semi-conductor material mounted therein, a whisker of conductive material mounted in said shell in point-contact relation with a surface of said crystal, a body of dielectric material embedding the contacting end of said whisker and said surface of said crystal, said body comprising a substantially uniform mixture of granular thermoplastic material and fluid thermosetting material solidified to form a rigid unit, and terminal means for said crystal and said whisker for connecting the same in an electrical circuit.

5. A point-contact crystal electrode device comprising a hollow shell having a crystal of semi-conductor material mounted therein, a whisker of conductive material mounted in said shell in point-contact relation with a surface of said crystal, a body of dielectric material embedding the contacting end of said whisker and said surface of said crystal, said body comprising a substantially uniform mixture of granular thermoplastic material and fluid thermosetting material solidified to form a rigid unit, said thermoplastic material constituting from 20% to by volume of the plastic material mixture, and terminal means for said crystal and said whisker for connecting the same in an electrical circuit.

6. A point-contact crystal electrode device comprising a hollow shell having a crystal of semi-conductor material mounted therein, a whisker of conductive material mounted in said shell in point-contact relation with a surface of said crystal, a body of dielectric material embedding the contacting end of said whisker and said surface of said crystal, said body comprising a substantially uniform mixture of a granular thermoplastic material and an inert filler material in a fluid thermosetting material, the mixture being solidified to form a rigid unit, and terminal means for said crystal and said whisker for connectin g the same in an electrical circuit.

7. A point-contact crystal electrode device comprising a hollow shell having a crystal of semi-conductor material mounted therein, a whisker of conductive material mounted in said shell in point-contact relation with a surface of said crystal, a body of dielectric material embedding the contacting end of said Whisker and said surface of said crystal, said body comprising a substantially uniform mixture or 25% by volume granular thermoplastic material, 25% by volume liquid thermosetting material, and 50% by volume granular inert filler material, mixed and solidified to form a rigid mass, and terminal means for said crystal and said Whisker for connecting the same in an electrical circuit.

8. A crystal diode comprising a hollow shell having a crystal of semi-conductor material fixedly mounted therein and electrically connected with a terminal at one of said shell, a conductive Whisker mounted in said body in point-contact relation with said crystal, terminal means for said whisker, and a dielectric body embedding the crystal contacting end portion of said Whisker and the adjacent surface of said'crystal, said body comprising a substantially uniform mixture of thermoplastic and ther mosetting materials united in an integral normally rigid 9. A crystal diode comprising a hollow shell having a crystal of semi-conductor material fixedly mounted therein and electrically connected with a terminal at one end of said shell, a conductive whisker mounted in said body in point-contact relation with said crystal, terminal means for said whisker, and a dielectric body embedding the crystal contacting end portion of said whisker and the adjacent surface of said crystal, said body comprising a mixture of granular thermoplastic material and liquid thermosetting material solidified in situ to form a normally rigid integral mass.

10. A crystal diode comprising a hollow shell having a semi-conductor crystal fixedly mounted therein and electrically connected with a terminal at one end of said shell, a conductive whisker extending into said shell from the opposite end thereof and having its inner end in pointcontact with said crystal, said whisker having a pair of axially spaced bends along its length and within said shell, a dielectric retainer body embedding the contact end of said Whisker and the adjacent surface of said crystal 1 end seal in said shell embedding the outermost and including the innermost one of the bends of said Whisker, said body comprising a mixture of granular thermoplastic material in a liquid thermosetting material solidified in situ to form an integral mass, and a solid bend of said Whisker.

11. In a crystal diode having a conductive Whisker in' point-contact relation with a crystal of semi-conductor material, a contact retaining means comprising a normally rigid-dielectric body embedding the contact end portion of said whisker and the adjacent surface of said crystal, said body comprising a mixture of granular thermoplastic material and fluid thermosetting material solidified in situ to form an integral mass.

12. In a crystal diode having a conductive whisker in point-contact relation with a crystal of semi-conductor material, a contact retaining means comprising a normally rigid dielectric body embedding the contact end portion of said Whisker and the adjacent surface of said crystal, said body comprising a mixture of granular polystyrene moulding material and a fluid thermosetting material solidified in situ to form an integral mass.

13. In a crystal diode having a conductive whisker in point-contact relation with a crystal of semi-conductor material, a contact retaining means comprising a normally rigid dielectric body embedding the contact end portion of said whisker and the adjacent surface of said crystal, said body comprising an integral cellular mass of thermosetting plastic material containing granules of thermoplastic material substantially uniformly dispersed throughout the mass.

References Qited in the file of this patent UNITED STATES PATENTS 1,537,856 Michels et a1 May 12, 1925 2,406,405 Salisbury Augf27, 1946 2,432,594 Thompson et al Dec. 16, 1947 2,472,938 Bnttain et a1 June 14, 1949 2,475,641 Rosenberg luly 12, 1949 2,572,801 Casellini Oct. 23, 1951 

